The present Invention relates to a zeolite composite membrane and a method for producing the zeolite composite membrane, and more specifically, a zeolite composite membrane having a zeolite membrane without cracks formed on a substrate and a method for producing the zeolite composite membrane.
There has been hitherto known a zeolite composite membrane having a zeolite membrane formed on a surface of a substrate. In addition, various methods for producing such a zeolite composite membrane have been proposed.
Japanese Patent Laid-Open 59-213615 discloses a substrate for a zeolite membrane in which a substrate of metal or the like is covered with ceramics of glass, mullite, and cordierite type, or alumina, silica, or minerals.
Japanese Patent Laid-Open 60-28826 discloses a composite membrane in which a thin membrane made of cage-shaped zeolite is united with a porous support of an inorganic or a high molecular substance on its surface. Good results have been obtained by the use of a support having high compatibility with a gel substance. For example, it is mentioned that a material No. 7930 from Corning Glass Works Co., Ltd., or one generally refired to as Vycor glass is particularly preferable as a support.
Japanese Patent Laid-Open 1-148771 relates to a method for crystallizing zeolite on a surface of a monolithic ceramic support and discloses a monolithic support having an oxide composition containing 45-4 wt % of silica, 8-45 wt % of alumina, and 7-20 wt % of magnesia, specifically, a sintered monolithic support made of cordierite, glass, or glass ceramic.
Japanese Patent Laid-Open 6-32610 relates to a method for producing an A-type or a faujasite-type zeolite membrane and discloses a substrate made of a substance containing silicon oxide as a main component. The method aims to improve bad adhesion to a substrate. A substrate itself is made of a material of a zeolite membrane in the method, and a surface of the substrate is covered with a zeolite membrane. Therefore, synthesis and impregnation can simultaneously proceed, and processes are simplified. Examples of a material of the substrate are borosilicate glass, quartz glass, silica alumina, and mullite.
Japanese Patent Laid-Open 9-173799 relates to a method for forming a loaded zeolite membrane and the membrane and discloses a substrate made of a ceramic substance basically containing alumina, zirconia, or titanium oxide; an inorganic, an organic, or a mixed substance selected from the group consisting of metal, carbon, silica, zeolite, clay and polymer.
Thus, zeolite composite membranes having a zeolite membrane on a surface of a substrate has conventionally been known. However, it has been found that these composite membranes have the following problem:
That is, as shown in FIG. 3, zeolite shows very complex characteristics in that zeolite has a very small thermal expansion coefficient at a temperature up to about 200xc2x0 C. and a negative coefficient at a higher temperature. Therefore, when a zeolite membrane is used at a temperature over 200xc2x0 C., difference in thermal expansion coefficient between the zeolite membrane and a substrate, for example, an alumina substrate extremely increases, thereby causing a crack in the zeolite membrane by a thermal stress.
Depending on kind of a zeolite membrane, it is required to add a template or a crystal directing agent upon synthesis. A zeolite membrane containing a template is subjected to calcination at about 500xc2x0 C. to remove the template. Since thermal expansion behavior of a zeolite membrane containing a template is remarkably different from that of a zeolite membrane containing no template (thermal expansion curve in FIG. 3 and thermal expansion curve in FIG. 4), a difference in thermal expansion between a zeolite membrane containing a template and a substrate, for example, an alumina substrate is extremely large, thereby causing a crack in the zeolite membrane due to thermal stress during calcination.
The present invention has been made in view of the conventional problems and alms to provide a zeolite composite membrane without any cracks by using a substrate having the same or a similar composition as a zeolite membrane upon forming a zeolite membrane on a surface of the substrate to almost equalize thermal expansion coefficients of the substrate and the zeolite membrane and a method for producing the zeolite composite membrane.
According to the present invention, there is provided a zeolite composite membrane comprising:
a zeolite membrane, and
a porous substrate made of a zeolite having the same or a similar composition as said zeolite membrane;
wherein said zeolite membrane is formed on said porous substrate.
According to the present invention, there is further provided a zeolite composite membrane intermediate comprising:
a zeolite membrane containing a template, and
a porous substrate made of zeolite having the same or a similar composition as said zeolite membrane and containing the same template as said zeolite membrane;
wherein said zeolite membrane is formed on said porous substrate.